International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators
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ADS/P4-15
Study of Subcriticality Control by Hf and Gd Hydrides for Accelerator Driven System K. Abe, T. Iwasaki, and Y. Tanigawa Tohoku University, Sendai, Japan Corresponding Author: kazuaki@neutron.qse.tohoku.ac.jp A major example of the Accelerator Driven System (ADS) is proposed by Japan Atomic Energy Agency (JAEA). The ADS is a hybrid system that consists of a high intensity proton accelerator, a spallation target of a heavy metal such as Lead-Bismuth Eutectic (LBE) and a sub critical core. The ADS has been researched for transmuting Minor Actinides (MA) and Long-Lived Fission Products (LLFP) in a High Level Waste (HLW). Subcriticality of the ADS is expected to be stable for keeping the thermal power constant. However, the subcriticality varies with the burn-up of fuel. The thermal power of the ADS must be kept by controlling the proton beam intensity. In the case of the ADS proposed by JAEA, the beam intensity is required to change it between about 20 to 30 mA in one operation cycle of 600 EFPD. The accelerator performance has been intense. At the high beam intensity, the irradiation damage is enhanced at the beam windows in the ADS. Therefore, subcriticality decrease should be moderated in one operation cycle of the ADS. In this paper, the control is studied by using a control rod (CR) or a burnable poison (BP) of metallic hydrides composed of Hf-hydride or Zr-Gd-hydrides. The CR of the Hf-hydride is expected as a long life-time in a fast reactor core. On the other hand, the BP of the Zr-Gd-hydrides is hopeful to keep the subcriticality constant without a control mechanism. Thus, the subcriticality control method by using the Hf and Zr-Gd hydride will be useful for controlling the subcriticality of the ADS. We supposed the absorber pins of the Hf-hydride or the Zr-Gd-hydride coated by stainless steel. The pins are set in a hexagonal assembly. The CR or BP assembly are arranged triangularly in an ADS core. For the CR and BP the analysis of core characteristics are performed for by using the continuous-energy Monte Carlo code, MVP, and the burn up calculation code, MVP-BURN. The evaluated nuclear data library, JENDL-3.3, is employed. As the result, the specification of the pins and the assemblies are designed adequately and the CR and BP assemblies can control the subcriticality in the ADS.
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